Bump flake8 from 3.9.2 to 4.0.1

Bumps [flake8](https://github.com/pycqa/flake8) from 3.9.2 to 4.0.1.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@3.9.2...4.0.1)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

{{cookiecutter.project_name}}/pyproject.toml

@@ -38,7 +38,7 @@ xdoctest = {extras = ["colors"], version = "^0.15.10"}
 sphinx = "^4.2.0"
 sphinx-autobuild = "^2021.3.14"
 pre-commit = "^2.15.0"
-flake8 = "^3.9.2"
+flake8 = "^4.0.1"
 black = "^20.8b1"
 flake8-bandit = "^2.1.2"
 flake8-bugbear = "^21.9.2"